Aero-Acoustic Optimization and Experimental Validation of a NACA 2415 Toroidal UAV Propeller

In defense and urban surveillance operations, small Unmanned Aircraft Systems (sUAS), specifically small-scale multirotors, have an important role. Their tactical stealth and flight endurance can be compromised by aerodynamic inefficiency and loud acoustic signatures. Standard injection-molded propellers prioritize manufacturing scalability over acoustic per- formance, generating excess tip vortices that lead to flight inefficiencies and degraded stealth performance. This research characterizes the aero-acoustic and propulsive performance of custom-made toroidal propellers using a NACA 2415 airfoil profile compared to a standard 6-inch (152.4 mm) 2-blade commercially available propeller. The toroidal geometry was modeled in SolidWorks using advanced lofting techniques, and the motor mount was simulated using topology optimization. The propeller was fabricated with Fused Deposition Modeling (FDM) on a Bambu Lab A1 printer, implementing a custom 99-wall slicing profile to maximize rotational isotropy. A motor mount for performing static thrust tests was designed and topology-optimized. The motor mount features a digital load cell and Arduino data logging system to analyze thrust and acoustic curves. Experimental results show that the 2-blade NACA 2415 propeller achieved a 3.5 dB reduction in noise and a 10.3% increase in static thrust generation at cruise (75% throttle) compared to the baseline propeller. During testing, the FDM-printed prototype propeller experienced delamination failure at 21,000 RPM (239 g thrust). Findings indicate that while implementing 2-blade and 3-blade toroidal geometries enhanced stealth and cruise performance for defense operations, the transition for deployment requires advanced materials like carbon-fiber-reinforced nylon (PA6-CF) to withstand these centrifugal loads.